Advanced Plasma Power Plasma Arc Fluidised Bed
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ADVANCED PLASMA POWER PLASMA ARC FLUIDISED BED GASIFICATION PLANT Advanced Plasma Power Limited Unit B2, Marston Gate Stirling Road South Marston Business Park Swindon SN3 4DE United Kingdom Tel: +44 (0)1793 238550 DDI: +44(0)1793 238546 Mobile: +44 7557 377801 [email protected] www.advancedplasmapower.com Plasma Arc Gasification Plants are economical in size compared to Mass Burn Incinerators er. co m The Gasplasma® Process Converts RDF feedstock into: •Converts 97% of the waste fuel •Very clean hydrogen-rich gas •Recyclable aggregate •Minimal emissions / low environmental impact •Negative carbon footprint •Potential CHP Energy efficiencies of >70% •Exporting up to 82% of electricity generated •Local waste, power and heat solution © 2010 Advanced Plasma Power Ltd Unit B2, Marston Gate, Stirling Road, South Marston Business Park, Swindon, Wiltshire SN3 4DE. T: 01793 238550 www.advancedplasmapower.com Briefing Document General Description Gasplasma® Process Advanced Plasma Power Process Description INTRODUCTION This document describes the process for a Gasplasma® facility that converts circa 150,000 tonnes per annum of Municipal Solid Waste (MSW) and commercial waste into electrical power and heat energy, exporting renewable electrical power to the national or local grid. This document also describes the core Gasplasma® process equipment and reviews how energy is produced from a waste feedstock. The Gasplasma® system is designed to be a part of an integrated waste processing system and is at the heart of a dedicated system that includes waste processing, drying, gasification, power and heat generation. FACILITY OVERVIEW The whole process can be viewed as three distinct operations (see Figure 1): Fuel Preparation The reception of waste and preparation of a Refuse Derived Fuel (RDF) Gas Production The conversion of the RDF to a syngas and inert solid aggregate product Power Generation Converting syngas to electricity and heat Fuel Preparation of RDF is based on a maximum design capacity of 150,000tpa of municipal and commercial wastes which, following processing to remove recyclate, moisture and reject materials, produces approximately 90,000 of RDF as feedstock for the Gasplasma® process. Syngas Production converts the RDF into a synthesis gas (syngas) through the Gasplasma® process which includes cooling, cleaning and conditioning of the syngas. During the syngas cooling stage, steam is produced and is used in the drying process and for power generation. Power Generation is achieved by converting the syngas into electrical power through reciprocating gas engines. Exhaust gases from the engines produce steam allowing further power generation to take place using a high efficiency steam turbine. Page 2 of 11 Advanced Plasma Power Process Description Waste Reception & Fuel Production RDF Recyclate Recovery Gasplasma® Syngas Production Power Generation Glass / Inert matls. Materials Syngas Cooling Non Ferrous Metals Gas Engines & Steam Turbine Dry Syngas Cleaning Ferrous Metals Wet Syngas Cleaning High Density Plastic Exhaust to Atmosphere Syngas Conditioning Moisture Rejects Figure 1 - Facility Overview FUEL PREPARATION Waste Reception The waste reception area receives waste deliveries during the agreed operating hours for the facility. All waste is deposited onto a tipping floor for initial visual screening. To allow for fluctuations in delivery volumes the waste reception area is designed to accommodate more than a days’ storage of waste while still leaving manoeuvring space for loading waste into the plant. The reception area accepts different waste types and incorporates options for pre-sorting and shredding of waste before feeding to the fuel preparation process. Suitable equipment including wheeled front end loaders and a 360 degree “excavator” moves the waste and carries out the stockpiling of materials within the reception area. Page 3 of 11 Advanced Plasma Power Process Description Fuel Preparation The facility is a single line plant with a nominal design processing rate of up to 25tph allowing up to 150,000tpa of material to be processed. The fuel preparation process operates for up to 24 hrs a day, 6 days per week, depending on the waste deliveries. The first stage of the fuel preparation system is the size classification of material through a rotary screen. The rotary screen then splits the materials into three size categories most suitable for the down stream equipment as follows (see Figure 2): Stream 1 Materials less than 15mm Stream 2 Materials from 15mm to 80mm Stream 3 Oversize Stream 1 is mainly dirt, grits, glass, stone and putrescibles. This material stream is transferred directly to containers and is then available for further processing or disposal. Stream 2 is the correct size range for the Gasplasma® process. Material which can be recycled is removed automatically to leave a feedstock with a high biodegradable content. Materials removed are glass, ferrous metals, non-ferrous metals and dense plastics. Following their removal the remaining materials are conveyed directly to the “wet” fuel store. This store acts as a process buffer store between fuel production and gas production. Stream 3 is oversize material which, as with Stream 2, is refined by removing recyclable material. The remainder is then passed through a shredder producing a particle size of less than 80mm. It is then combined with Stream 2 in the wet fuel store. Drying To improve the consistency of the fuel the material is dried using steam recovered from the Gasplasma® process. The design point of the final dry RDF is 12 -16 MJ/kg, 10-14% moisture and 14-18% ash. Approximately 90,000tpa of RDF is produced from the input tonnage of 150,000tpa. The moisture laden air removed from the RDF is treated to remove odour before release. Page 4 of 11 Advanced Plasma Power Process Description Figure 2 - Fuel Preparation GAS PRODUCTION The Gasplasma® system operates on a 24 hour/7 day week basis. At the heart of the facility is an advanced Gasplasma® thermal process that produces a syngas with a calorific value of between 10 and 14MJ/Nm3. The process produces a crude syngas which is treated to remove particulate matter, acid gases and volatile metal vapours. The cool, stable hydrogen-rich syngas which is produced can be used for power generation. Within this section of the facility there are four main process groups (see Figure 4): Page 5 of 11 Advanced Plasma Power Process Description Gasification Gas Cooling Dry Gas Cleaning Wet Gas Cleaning Gasification The Gasplasma® process is made up of two closely coupled but separate operations: Gasification of RDF Plasma Conversion of Gas Gasification of RDF RDF is fed into the gasifier under strictly controlled conditions. The process environment is maintained by control of oxygen, steam and RDF feed rate. This process provides sufficient heat to maintain the fluid bed temperature and produce a “crude syngas”. The syngas contains significant quantities of long chain hydrocarbons which would condense as tars and residues. The ash component of the RDF is removed from the base of the gasifier through the bed screening process and conveyed to a hopper where it is metered into the plasma converter. There are no residues, chars or ash removed at this stage of the process. Plasma Conversion of Gas The raw syngas is transferred from the gasifier to the plasma converter via a refractory lined duct. In the centre of the plasma converter is a graphite electrode from which a thermal plasma arc is generated (see Figure 3). The syngas is exposed to elevated temperatures and intense ultra violet light. The effect is to “crack” and reform the tars and chars contained in the syngas into its basic composition of hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2) and water (H20). Figure 3 - Image of a Thermal Plasma Arc The syngas is then drawn via a refractory lined duct to the inlet of the gas cooling system. At all times the gasifier and plasma converter operate at a negative pressure of <-5 to -10 mbar. Page 6 of 11 Advanced Plasma Power Process Description The plasma converter has been designed using computerised flow and modelling techniques to obtain maximum dwell time for the syngas within the converter whilst allowing time for ash and dust particles to drop out of gas stream. These particles are then incorporated into a molten melt which builds up in the base of the converter. The molten material is tapped from the converter and cooled for use as a vitrified and stable material. This material has been approved by the Environment Agency as a product and is trademarked under the name Plasmarok®. Gas Cooling System The gas cooling system comprises a heat recovery boiler designed to reduce syngas temperatures from circa 1200ºC to 200ºC and generates steam at 10bar pressure. The basis of the design is a water tube boiler, incorporating robust features as used throughout heavy industry with specific attention given to the materials of construction for long service life and to minimise down time caused by fouling and corrosion. The steam generated is used in the process at the drying and Gasplasma® stage. Dry Gas Cleaning System The gas cleaning system, operating at 180-220ºC, removes fine particulate materials from the gas stream, neutralises acidic gas and removes heavy metal vapour. The syngas passes to the ceramic particulate filter via an insulated duct into which sodium bicarbonate and activated carbon is injected. The duct provides sufficient residence time and turbulence to allow good reaction and collection, providing high capture rates for acidic components. Particulate matter is trapped on the ceramic filter elements and periodically removed using a nitrogen reverse pulse system. Wet Gas Cleaning System The syngas enters a quench vessel where the temperature is reduced using water sprays. It then enters a scrubber chamber and flows through two packed beds before being exposed to bio liquor that absorbs the hydrogen sulphide in the syngas. The bio liquor is passed to a bioreactor where it is aerated and dosed with small quantities of sodium hydroxide to maintain the pH and nutrients for the organisms.